The I2C page for the Adafruit Trinkey QT2040 guide has the image (above) which uses the terms controller and peripheral, the page also explains the nomenclature, and references the previous naming convention. This will appears on multiple pages on the Adafruit Learning System and Adafruit documention –

“Typically, there is a device that acts as a controller and sends requests to the peripheral devices on each bus. In this case, your microcontroller board acts as the controller, and the sensor breakout acts as the peripheral. Historically, the controller is referred to as the master, and the peripheral is referred to as the slave, so you may run into that terminology elsewhere; at this time, Adafruit refers to them as controller and peripheral.”

IEEE December 2020: IEEE SA Standards Board Resolutions …
“IEEE standards (including recommended practices and guides) shall be written in such a way as to unambiguously communicate the technical necessities, preferences, and options of the standard to best enable market adoption, conformity assessment, interoperability, and other technical aspirations of the developing standards committee. IEEE standards should be written in such a way as to avoid non-inclusive and insensitive terminology (see IEEE Policy 9.27) and other deprecated terminology (see clause 10 of the IEEE SA Style Manual) except when required by safety, legal, regulatory, and other similar considerations. Terms such as master/slave, blacklist, and whitelist should be avoided.”

Related:

• Micropython updating to “controller/peripheral” – June 2021.
• MOSI/MISO and 140 Years Of Wrong – June 2021.
• The Python programming language repository migrates to main on GitHub… May 2021.
• What Is the Best Way to Purge…
• Fight Over Offensive Terms in Computing – April/May 2021.
• IEEE SA Standards Board Resolutions – December 2020.
• The Linux kernel has now adopted inclusive language – JULY 12, 2020.
• Git and Branch Naming – Software Freedom Conservancy – June 2020.
• Making open source more inclusive by eradicating problematic language @redhat – JUNE 30, 2020.
• A Resolution to Redefine SPI Signal Names – Open Source Hardware Association – JUNE 29, 2020.
• Replacing Terms in Music Technology – JUNE 22, 2020.
• Renaming the default branch – GitHub.
• Replacing “master” reference in git branch names – May 2019.
• “Master” on GitHub – Feb, 2001.
• Black Lives Matter at Adafruit.